Document EP 0 744 246 discloses a calibration template of the kind mentioned above, which template is for mounting in the place of an ophthalmic lens on a machining device that is fitted firstly with two arms for blocking an ophthalmic lens, and secondly with a grindwheel having a beveling groove.
That calibration template is in the general form of a disk with an edge face that presents a hollow setback that defines two angular points.
On calibration, when the calibration template is blocked between the two blocking arms of the machining device, use is made of those angular points to determine the radial position and the angular position of the axis of the blocking arms relative to the axis of the grindwheel.
On its circular portion, the edge face of the calibration template also presents a zone of bevel-shaped cross-section.
During calibration, use is made of this bevel to determine the axial position of the beveling groove of the grindwheel relative to the axis of the blocking arms.
Although such a calibration template is found to be perfectly effective in calibrating the position of the grindwheel relative to the blocking arms, it is nevertheless found to be unsuitable for calibrating the positions of other tools that the machining device may include. In particular, it is unsuitable for calibrating the positions of a drill, of a grooving grindwheel, or indeed of a chamfering grindwheel fitted to the machining device.
In order to perform such calibration, the user of the machining device is thus constrained to call on competent technicians.
In order to perform calibration, such technicians generally make use of about twenty ophthalmic lenses to perform tests that are lengthy, tedious, and difficult, and that make it possible, after trial and error, to calibrate the positions of the drill, the grooving grindwheel, and the chamfering grindwheel of the machining device.